What is Sleep Apnea?
Sleep apnea is a disease. In simple terms, it is a
repeated decrease of airflow into the lungs during sleep.
In uncomplicated sleep apnea, the lungs are normal.

The airflow decreases are episodic.
That is, airflow into the lungs is normal except for
periods where it drops below a critical level. The drops last at least 10 seconds.

An adult with mild sleep apnea has 5 or more drops in airflow per
hour of sleep.
In the most severe cases, 100 or more such
drops may occur per hour of sleep.
Children are a different story.

The figures below illustrate airflow patterns during an hour of sleep.

Normal person

Mild sleep apnea

Severe sleep apnea

The middle figure shows 5 significant drops in airflow. In three of the drops, airflow falls to zero.
These are apneas. In two other drops, airflow is below the critical level, but
not zero. These are hypopneas (hi-pop-knee-uz). The middle figure also
shows one non-significant drop in airflow.

Many aspects of the definition of sleep apnea are still debated.
We have presented here a simplified introduction.